Understanding the Differences and Characteristics of BJT and FET in Electronics
Learn about the disparities between Bipolar Junction Transistors (BJT) and Field-Effect Transistors (FET) in this informative content. Explore the construction, operation, and characteristics of these semiconductor devices, including N-channel JFET specifics, operating behaviors such as pinch-off, drain characteristics, and transfer characteristics. Enhance your knowledge of current-controlled versus voltage-controlled devices, and delve into the unique attributes of npn, pnp, JFET, and MOSFET transistors.
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Presentation Transcript
By k. Sreevidya Asst .professor Dept of ECE
Difference between BJT & FET BJT FET Three terminal semiconductor device. Emitter, base, collector Current controlled device Bipolar device Two types- npn & pnp Three terminal semiconductor device Source, gate,drain Voltage controlled device Unipolar device Two types JFET & MOS FET
Construction of N-channel JFET Major part of the structure is n- type meterial. Top of the n-type channel Is connected through an ohmic contact to a terminal Reffered to as drain(D). As lower end Connected through an ohmic contact to a terminal Reffered as source (S). P-type meterials connected to gether and taken as terminal gate(G). JFET has two pn junctions under no bias condition.
JFET operating characteristics:VGS=0V Three things happen when Vgs=0v and Vds Is increased from 0v to more positive Voltage A depletion region between p-gate and N- channel increases as electrons from N-channel Combine with holes From p-gate. Increasing the depletion region decreasing the size of N-channel Which increases the resistance of the N-channel. Even through the N-channel resistance increasing the current (ID) from source to drain through the N-channel is increasing.This is because Vds is increasing.
JFET operating characteristics: pinch off If Vgs =0v and Vds is further increased to a more positive Voltage , that the depletion region gets increases and pinchoff the N- channel. This suggests that the current in N-channel (ID) would be dropped to SaturatIon.
JFET drain characteristics Plot between Vds Vs Id for different values of vgs. When Vgs=0v & Vds is positive ,Id increases linearly. When Vds is more positive Voltage id gets saturated as Idss. When Vgs=-ve ,& Vds positive Voltage Id current reduces from the previous value of Id.
JFET TRANSFER CHARACTERISTICS Plot between vgs and id for fixed value of vds When vgs = 0v id is idss and as vgs more negative ,the drain current Id reduces.
